Various types of moisture curable sealant materials are known in the art. A particularly useful material is a polysiloxane having silicon end groups provided with one or more hydrolyzable groups. This polymer vulcanizes rapidly by contact with atmospheric moisture without producing undesirable phenomena such as bubbling caused by generation of gaseous reaction products. Moreover, the adhesive property and the thermal stability of this polymer are excellent. However, since such a polymer has a polysiloxane backbone, its cost is higher than might be desired. Accordingly, efforts have been made recently to develop lower cost polymers having hydrocarbon backbones and having silicon atoms with a hydrolyzable end group only at each end of the molecule.
One such lower cost polymer is disclosed in U.S. Pat. No. 3,971,751. This patent discloses a polyether compound having a silylether terminal group at each end of the molecule of the '751 patent is made by polymerizing an alkylene oxide in the presence of an alcohol, such as propylene glycol or ethylene glycol. However, since caustic was used to catalyze the polymerization reaction, the molecular weight of the diol is limited to about 3,000, and above this molecular weight the functionality decreases significantly, as does the physical properties of the cured polymer product. Therefore, in order to obtain the necessary physical properties these diols were coupled with a dihalo-organic compound in order to increase the molecular weight of the diol. Unfortunately, oligomerization reactions tend to occur in the presence of the dihalo-organic compound, and the degree of polymerization and the molecular weight distribution (or so-called "polydispersity") of the resulting polymer is quite broad. This high polydispersity polyol is then converted to a polymer having terminal unsaturation at each end by reaction of the polyol with a compound such as allyl chloride. Overall, the process of this '751 process is cumbersome and costly. Accordingly, new processes for Producing polymers characterized by lower polydispersity values would be highly desired by the sealants and adhesives community.
As another illustration, European Patent Application 397,036 discloses the preparation of an unsaturated group-terminated polyalkylene oxide by subjecting a monoepoxide having at least 3 carbon atoms to a ring-opening addition polymerization using an initiator in the presence of a double metal cyanide complex catalyst, followed by converting the terminal hydroxyl groups of the resulting hydroxyl group-terminated polyalkylene oxide to unsaturated groups by an end-capping procedure. Example 1 of this European Patent Application discloses the polymerization of propylene oxide using an allyl alcohol initiator in the presence of a zinc hexacyano cobaltate (DMC) catalyst to produce a "monol" (a mono-alcohol), followed by reaction with allyl chloride to covert the terminal hydroxyl group on the monol to an unsaturated group, followed by an addition reaction with methyldimethoxysilane to provide a polyalkylene oxide terminated at each end with a hydrolyzable silane group.
New processes and compositions for providing inexpensive alternatives to the use of polysiloxanes for the production of moisture curable sealants characterized by excellent elongation properties would be highly desired by the sealants and adhesives manufacturing community.